Scientists find hormone that controls sugar, alcohol cravings

Still desperate for another candy bar or cocktail, but don’t know why? Never fear - US scientists have found a liver hormone that could curb our sugar and alcohol cravings, and help those suffering from diabetes or obesity.

Two independent research groups have found a hormone produced by the liver (fibroblast growth factor 21, or FGF21) that suppresses the desire to consume simple sugars, the studies published in Cell Metabolism suggest.

The hormone is produced if the level of carbohydrates is high, in which case it enters the bloodstream and sends a signal to the brain to curb the craving.

The findings are unprecedented, researchers say. Earlier, only appetite-controlling hormones were known.

"This is the first liver-derived hormone we know that regulates sugar intake specifically," said Matthew Potthoff, assistant professor of pharmacology at the University of Iowa, and co-senior author of one of the papers.

"We never imagined that a circulating, liver-derived factor would exist whose function is to control sweet appetite,” his co-senior author Matthew Gillum, of the University of Copenhagen, added. "We are very excited about investigating this hormonal pathway further."

One reason FGF21 exists in animals could be to improve diet quality, the scientists said. Another possibility, since sugar can ferment, was that it helped the liver protect itself from excess alcohol.

"FGF21 can exert powerful effects on behavior by acting on the central nervous system, including in humans," Steven Kliewer of University of Texas Southwestern Medical Center, and senior author of the other study, said.

How can the discovery be used?

First and foremost, the findings can help people with diabetes, as well as those “who might not be able to sense when they've had enough sugar, which may contribute to diabetes,” according to co-first author Lucas BonDurant.

In one of the studies, researchers used genetically-engineered mice, injecting FGF21 and giving the mice a choice between a normal diet and a sugar-enriched diet. As a result, the mice didn’t stop eating sugary foods altogether, but ate seven times less.

In a different experiment, scientists studied genetically-modified mice that either didn't produce FGF21 at all, or produced over 500 times more of the hormone than normal mice. The former ate more sugar, while the latter consumed less, researchers found.

The same hormone suppresses the consumption of sweets in primates, another study discovered. A single dose could cause a monkey to almost immediately lose interest in sweet water, researchers said, adding that they were struck by the powerful effect of FGF21.

All in all, the study concluded that FGF21 decreases appetite and intake of sugar.

Now scientists want to find out the exact neural pathways that regulate FGF21's ability to manage macronutrient preference.

"In addition to identifying these neural pathways, we would like to see if additional hormones exist to regulate appetite for specific macronutrients like fat and protein, comparable to the effects of FGF21 on carbohydrate intake," Potthoff said.

Kliewer, however, has cautioned against pronouncing the findings a panacea for suppressing sugar and alcohol consumption: "It's important to keep in mind that these reward behaviors are closely tied to mood, and so additional studies to determine if FGF21 causes depression are certainly warranted," he said.